Richard, what would be more relevant is to crop all the images the same size. For example, the same size as the 50D shot. That is what happens in focal lenght challenged situations. One needs or desires a tight crop so the images from the 5DII and 1D3 would get cropped. How does that compare to a higher pixel density sensor? The images posted do not address the OP's question:

"If I were to capture an image of the same bear from the same distance with each body & 500 mm lens, then crop the full frame image so that the bear is the same size as in the 7D image - or crop both images so that the bear is the same size - will the "quality" of the bear image be essentially the same when printed?"

Since these shots are all varying FOV, nothing can be directly compared.